The present invention relates to a communication device having a facsimile function.
As a conventional communication device, there has been proposed a facsimile device capable of communicating with another facsimile device connected thereto through an analog public telephone line (network) according to the ITU-T standard T.30 (refer to Patent Reference).    Patent Reference: Japanese Patent Publication No. 2003-259098
The conventional communication device starts communication through the following communication protocol. First, the conventional communication device sends a call signal (a CNG signal) to another facsimile device for sending image data to the facsimile device. After the conventional communication device sends the CNG signal, when the conventional communication device receives a digital identification signal (a DIS signal) from the facsimile device indicating a reception capability thereof, the conventional communication device determines a transmission mode (a transmission speed, a size of the image data, and the likes) for transmitting the image data according to the reception capability of the facsimile device and a transmission capability of the conventional communication device. Then, the conventional communication device sends a digital command signal (a DCS signal) to the facsimile device to notify the transmission mode.
In the next step, the conventional communication device sends a training check signal (a TCF signal) to the facsimile device at the transmission speed thus notified to start a modem training, thereby determining whether the facsimile device is capable of receiving the image data at the transmission speed notified with the DCS signal. When the conventional communication device receives a reception ready confirmation signal (a CFR signal) from the facsimile device indicating reception of the TCF signal, the conventional communication device sends the image data to the facsimile device.
On the other hand, when the conventional communication device receives a training failure signal (a FTT signal) from the facsimile device indicating that the facsimile device fails to receive the TCF signal, the conventional communication device adjusts the transmission speed to a slower transmission speed by a specific decrement set in advance due to a modem training failure. Then, the conventional communication sends the DCS signal to the facsimile device for notifying the adjustment of the transmission speed.
Afterward, the conventional communication sends the TCF signal to the facsimile device at the transmission speed thus adjusted. The conventional communication device adjusts the transmission speed, and repeatedly sends and receives the DCS signal and the TCF signal until the conventional communication device receives the CFR signal from the facsimile device.
When an IP (Internet Protocol) telephone adaptor is used, the conventional communication device is connected to an IP network. Accordingly, the conventional communication device is capable of transmitting and receiving various signals and image data to and from a facsimile device through the IP network. When the IP telephone adaptor receives image data having a large file size from the conventional communication device, the IP telephone adaptor divides the image data into a plurality of packets, and transmits the packets to the facsimile device through the IP network.
In the IP network, different from the analog public telephone network, in which one single route is used for transmitting data, a plurality of routes is used for transmitting various signals and a plurality of packets. When a large number of devices connected to the IP network transmit and receive various signals and image data while sharing a plurality of routes, the IP network tends to be crowded. To this end, the IP network has a configuration, in which various signals and packets are temporarily stored in a queue of a router and an accumulation exchange portion, thereby alleviating the congestion of the routes.
In the IP network, when various signals and packets newly arriving queues exceed various signals and packets transmitting to the IP network from the queues, a conflict may occur due to delay in a packet transmission process for waiting for a queue or a large volume of packets, thereby significantly fluctuating the transmission speed of packets.
As described above, in the IP network, the transmission speed of packets may be significantly fluctuated irregularly. Accordingly, when the conventional communication device is communicating with the facsimile device through the IP network, and the conventional communication device adjusts the transmission speed similar to the facsimile communication to the facsimile device through the analog public telephone line, a volume of packets may change when the modem training is performed and when the image data are transmitted. As a result, packets of the image data transmitted at the transmission speed thus adjusted become a queue waiting state, and are not transmitted within a specific period of time from a queue, thereby causing timeout. When the timeout occurs, the conventional communication device is not able to transmit the image data to the facsimile device, thereby causing an error.
In view of the problems described above, an object of the present invention is to provide a communication device capable of solving the problems of the conventional communication device. In the communication device of the present invention, it is arranged to switch between two types of communication sequences having difference communication capabilities. Accordingly, it is possible to smoothly transmit and receive various signals and image data to and from a facsimile device connected to an IP network.
Further objects and advantages of the invention will be apparent from the following description of the invention.